1. Field of Technology
The present invention relates to a roll paper printer having a roll paper size detection device featuring improvement enabling easy replacement of the roll paper.
2. Description of Related Art
One type of roll paper printer has the roll paper loaded so that the roll paper can simply roll on the bottom of the roll paper compartment. The roll paper typically has a long tape of recording paper wound into a roll on a hollow core that has a hole in the center. This type of roll paper printer also commonly has a roll paper size detection device for detecting the near-end of the roll when there is little roll paper left on the core. One type of roll paper size detection device has a lever that is inserted to the hole in the core of the roll paper.
This lever is pressed by an urging member against the round end (side) of the roll paper held in the roll paper compartment at a predetermined height above the bottom of the roll paper compartment. When the outside diameter of the roll paper gradually decreases as the paper is consumed by printing, the position of the core hole also gradually descends. When the amount of roll paper decreases so that the core hole has descended to the predetermined height, the detection lever slips off the round end of the roll paper and is inserted to the roll paper core. The detection lever is not limited to a mechanism that inserts the lever to the roll paper core, and can be a mechanism causing the lever to separate in the direction of the outside circumference of the roll from the round end of the roll. That the amount of remaining roll paper is low can be known by using a mechanical or other type of detection switch to detect movement of such a detection lever that separates from the round end of the roll paper into the core hole or to the outside surface of the roll.
A recessed channel into which the roll paper is dropped once the diameter has become small, and inclined guide surfaces for guiding the roll paper into this channel, are formed in the bottom of the roll paper compartment. By guiding the roll paper along these sloped surfaces into the recessed channel, the roll paper can be held at a position that can be detected by the detection lever, and the near-end of the roll paper can be reliably detected.
JP-A 9-254474 and JP-A 2003-11453 teach a roll paper printer having a roll paper compartment and a roll paper size detection device that use this type of detection lever to detect the near-end of the roll paper.
When there is no roll paper in the roll paper compartment, the detection lever of the roll paper detection device protrudes into the roll paper detection compartment. When loading the roll paper, such as when replacing the roll paper, the user must therefore push and retract the detection lever from the roll paper compartment using the end of the roll paper in order to place the roll paper into the roll paper compartment. If the detection lever is inserted to the core hole when removing the roll paper, the detection lever must also be pushed to the side and retracted so that the roll paper can be removed.
If the roll paper is loaded or removed quickly when loading or removing the roll paper, the detection lever may not be able to retract as quickly, resulting in the detection lever catching on the roll paper and interfering with loading and removing the roll paper. The detection lever may even be damaged.
In order to make loading and removing the roll paper easier, a taper with a large angle in the roll paper loading and removal direction must be included on the detection lever so that the detection lever can be pushed and retracted smoothly. However, rendering a taper with a large angle on the detection lever causes the problem of a drop in detection precision because setting the point at which the detection lever is inserted to the roll paper core with precision when the roll paper decreases to a predetermined remaining volume is more difficult than with a detection lever that does not have a taper. The same problem also occurs with a mechanism whereby the detection lever separates to the outside circumference of the roll paper.